Shaped body of calcium silicate and process for producing same

ABSTRACT

A calcium silicate shaped body which comprises a multiplicity of interconnected secondary particles of calcium silicate crystals, voids interspersed between the secondary particles, and at least one inorganic inactive substance selected from among carbonaceous substance, carbide, nitride, silicide and metallic oxide which is physically united with the secondary particles, the shaped body containing the inactive substance in an amount of 21 to 70% by weight; and a calcium silicate shaped body which comprises a multiplicity of interconnected secondary particles of calcium silicate crystals, voids interspersed between the secondary particles, and at least one inorganic inactive substance selected from among carbonaceous substance, carbide, nitride, silicide and metal oxide and physically united with the secondary particles, and an amorphous siliceous substance.

TECHNICAL FIELD

The present invention relates to novel shaped bodies of calcium silicatehaving outstanding heat insulating properties and to a process forproducing the same.

BACKGROUND ART

Calcium silicate shaped bodies are lightweight, have excellent heatinsulating properties, high fire resistance and various othercharacteristics, and are therefore widely used.

In the field of heat insulating materials and the like, there is ademand for calcium silicate shaped bodies of improved heat insulatingproperties in recent years.

Accordingly processes have been proposed for giving improved heatinsulating properties by incorporating various substances into calciumsilicate shaped bodies.

U.S. Pat. No. 3,001,882 discloses a process for producing a shaped bodyhaving improved heat insulating properties at a high temperature (288°C., 550° F.) by adding a chemically inactive substance to a startingslurry composed of a calcareous material, a siliceous material andwater, shaping the slurry, and subjecting the green shaped body obtainedto a hydrothermal synthesis reaction. With this process, however, thestrength of the shaped body tends to decrease with an increase in theamount of inactive substance used. Especially when the amount exceeds20% by weight of the shaped body, the shaped body obtained isexceedingly low in strength and is not usable. Thus, although theprocess wherein the green shaped body is subjected to hydrothermalsynthesis reaction gives improved heat insulating properties at a hightemperature, the improvement is inherently limited and is stillinsufficient, while the process fails to afford improved heat insulatingproperties at low temperatures of up to about 200° C.

Unexamined Japanese Patent Publication No. SHO 58-145652 discloses (a) aprocess for producing a shaped body by preparing a slurry of calciumsilicate crystals first, adding to the slurry a substance which absorbsor diffuses radiant energy, shaping the resulting slurry and drying theshaped body: (b) a process for producing a shaped body of calciumsilicate crystals by preliminarily reacting a starting slurry to obtaina slurry of C-S-H (I) which is a precursor of crystalline calciumsilicate, adding the above substance to the slurry, shaping the slurryand curing the green shaped body with steam: and (c) a process forproducing a shaped body of calcium silicate crystals by preliminarilyreacting a starting slurry containing the above substance to obtain aslurry of C-S-H (I), shaping the slurry and curing the green shaped bodywith steam. However, the processes (a) and (b) are unable to produce auseful lightweight shaped body because of seriously reduced strength ifmore than 20% by weight of the substance is present based on the shapedbody, while the process (c) encounters difficulties in producing ashaped body itself owing to deformation or shrinkage if not smaller than15% by weight of the substance is used. Further although these processesachieve some improvement in the heat insulating properties of the shapedbody at high temperatures of at least 300° C., the improvement is stillinsufficient, whereas the processes fail to attain any substantialimprovement in the heat insulating properties at low temperatures of upto about 200° C.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a novel shaped body ofcalcium silicate which is lightweight and has outstanding heatinsulating properties over a wide temperature range of from low to hightemperatures, and also a process for producing the shaped body.

Another object of the present invention is to provide a novel shapedbody of calcium silicate which is lightweight and has outstanding heatinsulating properties over a wide temperature range while retainingfully satisfactory strength for use, and a process for producing thesame.

Other features of the present invention will be made apparent from thefollowing description.

The present invention provides a calcium silicate shaped body whichcomprises a multiplicity of interconnected secondary particles ofcalcium silicate crystals, voids interspersed between the secondaryparticles, and at least one inorganic inactive substance selected fromamong carbonaceous substance, carbide, nitride, silicide and metallicoxide and physically united with the secondary particles, the shapedbody containing the inactive substance in an amount of 21 to 70% byweight. The present invention further provides a calcium silicate shapedbody which comprises a multiplicity of interconnected secondaryparticles of calcium silicate crystals, voids interspersed between thesecondary particles, at least one inorganic inactive substance selectedfrom among carbonaceous substance, carbide, nitride, silicide andmetallic oxide and physically united with the secondary particles, andan amorphous siliceous substance.

Our research has revealed that when a shaped body already developed bythe present applicant and disclosed in U.S. Pat. No. 3,679,446 comprisessecondary particles of a large number of interconnected calcium silicatecrystals and at least 21% by weight of at least one inorganic inactivesubstance selected from among carbonaceous substance, carbide, nitride,silicide and metallic oxide and physically united with the secondaryparticles, the shaped body has the following novel features:

(1) despite the presence of the specific inactive substance in an amountof at least 21% of the weight of the shaped body, the shaped body islightweight and retains fully satisfactory strength for use,

(2) the shaped body has remarkably improved heat insulating propertiesat high temperatures of at least 200° C., and

(3) the shaped body has remarkably improved heat insulating propertiesalso at lower temperatures of up to 200° C.

Our research has further revealed that when the shaped body of theabove-specified structure has incorporated an amorphous siliceoussubstance therein, the shaped body exhibits more improved heatinsulating properties especially at low temperatures of up to 200° C.without any substantial reduction in the strength despite the presenceof the amorphous siliceous substance.

Our research has further revealed that the presence of the amorphoussiliceous substance produces the above effect still to a remarkableextent even if the content of the inactive substance is less than 21% byweight, and that in this case the effect of the inactive substance toimprove the heat insulating properties especially at high temperaturescombines with the effect of the amorphous siliceous substance to improvethe heat insulating properties especially at low temperatures to producean overall effect to give greatly improved heat insulating propertiesover a wide temperature range. The present invention has beenaccomplished based on the above findings.

The shaped body of calcium silicate of the present invention can bebasically produced, for example, according to the process for producingcalcium silicate shaped bodies disclosed in U.S. Pat. Nos. 3,501,325 or3,679,446 wherein a starting slurry containing a siliceous material, acalcareous material and water is subjected to a hydrothermal synthesisreaction with heating and stirring at an elevated pressure to prepare anaqueous slurry of secondary particles of calcium silicate crystals,followed by shaping and drying. In the above process the shaped body ofthe present invention can be prepared by the method characterized inthat a specific amount of the specified inactive substance is added tothe starting slurry, or the inactive substance is added to the startingslurry and further admixing the amorphous siliceous substance is addedto the aqueous slurry resulting from the hydrothermal reaction.

More specifically, the present invention provides a process forproducing a calcium silicate shaped body by subjecting a starting slurrycontaining a siliceous material, a calcareous material and water to ahydrothermal synthesis reaction with heating and stirring at an elevatedpressure to obtain an aqueous slurry of secondary particles of calciumsilicate crystals, followed by shaping and drying, the process beingcharacterized by adding to the starting slurry at least one inorganicinactive substance selected from among carbonaceous substance, carbide,nitride, silicide and metallic oxide to cause the inactive substance tophysically unite with the secondary particles by the hydrothermalsynthesis reaction, and using the inactive substance in an amount of 21to 70% by weight based on the shaped body. The invention also provides aprocess for producing a calcium silicate shaped body by subjecting astarting slurry containing a siliceous material, a calcareous materialand water to a hydrothermal synthesis reaction with heating and stirringat an elevated pressure to obtain an aqueous slurry of secondaryparticles of calcium silicate crystals, followed by shaping and drying,the process being characterized by adding to the starting slurry atleast one inorganic inactive substance (hereinafter referred to as"inactive substance") selected from among carbonaceous substance,carbide, nitride, silicide and metallic oxide to cause the inactivesubstance to physically unite with the secondary particles by thehydrothermal synthesis reaction, and admixing an amorphous siliceoussubstance with the aqueous slurry of calcium silicate crystals.

Our research has revealed that when the inactive substance is added tothe starting aqueous slurry before the hydrothermal synthesis reactionwhich is to be conducted with stirring, the inactive substancephysically unites with the secondary particles of calcium silicatecrystals, so that the inactive substance can be incorporated in a largeamount into the shaped body to be prepared from such secondary particleswhile permitting the shaped body to have lightweightness and fullysatisfactory strength for use. We have further found that the amorphoussiliceous substance, when to be used, can be added after thehydrothermal synthesis reaction almost without entailing any reductionin the strength of the resulting shaped body and consequently that whenthe inactive substance is added before the hydrothermal reaction withamorphous siliceous substance added after the reaction, the shaped bodycan be given more greatly improved heat insulating properties over awide temperature range than when the inactive substance is used singly,without substantially impairing the strength of the shaped body. Theproduction processes of the present invention have been accomplishedbased on these findings.

The shaped body of the present invention, which has fully satisfactorystrength for use, has over a wide temperature range a greatly reducedthermal conductivity afforded by a large amount of inactive substancepresent singly or by a combined use of the inactive substance with theamorphous siliceous substance.

The shaped body of the present invention is improvement of one disclosedin U.S. Pat. No. 3,679,446. The improvement is in that the inactivesubstance is present in a special state or in combination with theamorphous siliceous substance. More specifically, the shaped body of thepresent invention consists essentially of a multiplicity ofinterconnected secondary particles of calcium silicate crystals andvoids interspersed between the secondary particales and furthercomprises the inactive substance which is physically united with thesecondary particles. This gives fully satisfactory strength for use andyet permits presence of a large amount of the inactive substance.

Each of the secondary particles of calcium silicate crystals isoriginally in the form of a substantially globular shell formed ofthree-dimensionally interlocked calcium silicate crystals and having anoutside diameter of about 5 to about 150 μm. The secondary particles ofcalcium silicate crystals are present in the shaped body as compressedin at least one direction by the shaping pressure. The inactivesubstance is physically united with the secondary particles as enclosedin the secondary particles. An observation under an optical microscopeas well as under a scanning electron microscope reveals that the shapedbody of the present invention has the structure described.

The above mode in which the inactive substance is present isattributable to the fact that the inactive substance, which is added tothe aqueous slurry before the hydrothermal synthesis reaction to beconducted with stirring, is physically united with secondary particlesof calcium silicate crystals as enclosed therein when the secondaryparticles are formed. This is apparent from an optical microscopicobservation of the aqueous slurry of secondary particles of calciumsilicate crystals, e.g., from FIG. 1 and FIG. 2. FIG. 1 is an opticalphotomicrograph (at a magnification of 250×) of an aqueous slurry ofsecondary particles of calcium silicate crystals which is free of anyinactive substance and serving as a control (one used for preparingspecimen No. 1 of shaped body in Example 1). FIG. 2 is an opticalphotomicrograph (at a magnification of 250×) of an aqueous slurry ofsecondary particles of calcium silicate crystals obtained with additionof rutile before hydrothermal synthesis reaction according to theinvention (one used for preparing specimen No. 3 of shaped body inExample 1). FIGS. 1 and 2 show that rutile added before the reaction isphysically united with the secondary particles as enclosed therein. Therutile is not physically united with the secondary particles when addedafter the hydrothermal reaction.

The shaped body of the present invention is prepared basically by thesame process as those disclosed in U.S. Pat. No. 3,679,446 and U.S. Pat.No. 3,501,325 on which the former patent is based, with the exception ofusing the inactive substance and/or the amorphous siliceous substance.

Any of siliceous materials which have heretofore been used for producingcalcium silicate shape bodies is advantageously usable as such for thepresent invention. Examples thereof are crystalline siliceous materialssuch as siliceous stone, siliceous sand, etc., and amorphous siliceousmaterials such as silica gel, silica flour (such as ferrosilicon dust,etc.), white carbon, diatomaceous earth, silica obtained by reactingaluminum hydroxide with hydrosilicofluoric acid resulting as aby-product from the wet process for preparing phosphoric acid, etc. Thecalcareous material can be any of those heretofore used, such as quicklime, slaked lime, carbide residuum, etc.

The CaO/SiO₂ mole ratio of the calcareous material to the siliceousmaterial is about 0.70 to about 0.90 when tobermorite crystals are to besynthesized, or about 0.90 to about 1.15 when xonotlite crystals are tobe obtained.

According to the present invention, an inactive substance and water areadded to the siliceous material and the calcareous material to prepare astarting slurry.

The inactive substance to be used in this invention is at least one ofcarbonaceous substances, carbides, nitrides, silicides and metallicoxides. Examples of useful inactive substances are carbonaceousmaterials such as active carbon, charcoal, coal, carbon black andgraphite; carbides such as silicon carbide, boron carbide and titaniumcarbide; nitrides such as silicon nitride, boron nitride and titaniumnitride; silicides such as calcium silicide; and metallic oxides such asiron oxides (hematite, magnetite, etc.), titanium oxides (rutile, etc.),tin oxides, manganese oxides, zirconium oxides, ilmenite, zircon andchromite. These substances are usable singly, or at least two of themcan be used in mixture. It is suitable that the inactive substance beusually about 0.001 to about 120 μm, preferably 0.001 to 100 μm, inparticle size.

The amount of inactive substance to be used in this invention differsdepending on whether the amorphous siliceous substance is usedconjointly therewith.

When a remarkable reduction is to be achieved in the thermalconductivity over a wide temperature range in the absence of theamorphous siliceous substance, the inactive substance needs to bepresent in a large amount. In this case, accordingly, the amount is suchthat the shaped body will contain 21 to 70% by by weight, preferably 25to 55% by weight, of the inactive substance. Conventionally, it has beenimpossible to use such a large amount of inactive substance since markedlower strength will then result, whereas even if a large amount is usedaccording to the invention, the resulting shaped body retains fullysatisfactory strength and is given the unique effect afforded by thepresence of the large amount, i.e. improved heat insulating propertiesover a wide temperature range of from low to high temperatures. Below21% by weight, the improvement in heat insulating properties is achievedto some extent at high temperatures but is almost unavailable at lowtemperatures. Above 70% by weight, radiation heat transfer is inhibitedbut increased heat transfer through the solid of the inactive substanceoccurs to totally result in an insufficient improvement in heatinsulating properties. Difficulty is further encountered in givinglightweight shaped bodies because of reduced bending strength.

The amorphous siliceous substance, when used, affords improved heatinsulating properties especially at low temperatures, whereby animprovement is achieved in the heat insulating properties over a widetemperature range even if the inactive substance is used in a smalleramount. In this case, therefore, the inactive substance is used in suchan amount that the resulting shaped body will contain about 2 to about60% by weight, preferably 5 to 50% by weight, of the inactive substance.Below 2% by weight, an insufficient improvement of heat insulatingproperties will result at high temperatures even when the amorphoussiliceous substance is used conjointly, whereas above 60% by weight, theincrease in the combined amount of the inactive substance and theamorphous siliceous substance gives reduced bending strength to theshaped body and results in the tendency that it becomes difficult toobtain lightweight shaped bodies.

According to the present invention, it is required to incorporated theinactive substance into the starting slurry to be subjected to ahydrothermal synthesis reaction. This permits the presence of a largeamount of the inactive substance without entailing a great reduction inthe strength. The inactive substance, when added after the reaction,results in a marked reduction in strength of the shaped body, e.g., inthe bending strength thereof.

The starting slurry may have further incorporated therein knownadditives. Examples of such additives are inorganic fibrous materialssuch as asbestos and rock wool.

The amount of water to be used for preparing the starting slurry is atleast 5 times, preferably 10 to 50 times, the amount by weight of thesolids of the slurry. When a lightweight body of about 0.1 g/cm³ in bulkdensity is to be produced, it is suitable that the amount by 15 to 50times, preferably 20 to 40 times, the amount by weight of the slurrysolids.

The starting slurry thus prepared is then subjected to a hydrothermalsynthesis reaction with stirring. The reaction is conducted at asaturated water vapor pressure usually of at least 4 kg/cm², preferably6 to 30 kg/cm². This reaction produces a slurry of secondary particleshaving an outside diameter of about 5 to about 150 μm and composedpredominantly of three-dimensionally interlocked tobermorite crystalsand/or xonotlite crystals, the secondary particles having the inactivesubstance physically united therewith as enclosed therein, the slurrycontaining the secondary particles as uniformly dispersed in water.

According to the present invention, the aqueous slurry containing thelarge amount of inactive substance may be shaped as it is or afterhaving incorporated therein the amorphous siliceous substance for givingfurther improved heat insulating properties at low temperatures. Whenthe content of the inactive substance is less than 21% by weight basedon the shaped body to be obtained, it is necessary to admix theamorphous siliceous substance with the slurry before shaping. In eithercase, a shaped body is obtained of course with remarkably improved heatinsulating properties over a wide temperature range.

The siliceous substance to be added in this invention as required needsto be amorphous. If crystalline siliceous substances are used, improvedheat insulating properties are not available. Further it is necessary toadd the amorphous siliceous substance to the slurry of secondaryparticles of calcium silicate crystals resulting from the hydrothermalsynthesis reaction. This combines the effect of the inactive substanceto give improved heat insulating properties with the effect of theamorphous siliceous substance to give improved heat insulatingproperties, consequently affording improved heat insulating propertiesover a wide temperature range.

Examples of useful amorphous siliceous substances are white carbon,ferrosilicon dust, silicon dust, silica gel, diatomaceous earth, flyash, etc. These substances are usable singly, or at least two of themcan be used in combination. Preferably usable as silica gel is Opsil-IIdisclosed in U.S. Pat. No. 4,230,765 (Examined Japanese PatentPublication No. SHO 55-14809) and already developed by the presentapplicant, i.e., secondary particles of high-purity porous silica gelhaving shapability. As disclosed in U.S. Pat. No. 4,230,765, Opsil-IImeans secondary particles of high-purity porous silica gel obtained bycarbonating secondary particles of calcium silicate crystals in thepresence of water to convert the calcium silicate into silica gel andsuperfine particulate calcium carbonate and subsequently treating theproduct with an acid.

It is suitable that the amorphous siliceous substance to be used beusually about 0.001 to about 150 μm, preferably 0.001 to 100 μm, inparticle size.

The amorphous siliceous substance is used in such an amount that theresulting shaped body will contain about 2 to about 60% by weight,preferably 5 to 50% by weight, of the substance. If the amount is lessthan 2% by weight, a sufficient improvement will not be achieved in theheat insulating properties at low temperature, whereas above 60% byweight, the shaped body obtained tends to exhibit a markedly reducedbending strength, hence objectionable.

Further the combined amount of the inactive substance and the amorphoussiliceous substance to be used in this invention is preferably about 4to about 70% by weight, more preferably 10 to 50% by weight, based onthe shaped body. If the amount is less than 4% by weight, there is thetendency that fully improved heat insulating properties will not beobtained over a wide temperature range, whereas above 70% by weight,markedly reduced bending strength will result, hence undesirable.

Accordingly to the present invention, various additives may further beadmixed with the slurry to be shaped. Examples of useful additives are awide variety of those which are used for preparing calcium silicateshaped bodies, such as fibers, clays, cements, binders, etc.

According to the present invention, the aqueous slurry comprisingsecondary particles of calcium silicate crystals and inactive substanceand further containing other additives when required, or a mixtureobtained by admixing the amorphous siliceous substance with the slurryis shaped by a usual method, for example, by dewatering by pressmolding, centrifugation or the like, and thereafter dried to obtain ashaped body of calcium silicate. When required, the aqueous slurry ormixture containing the inactive substance and prepared as above isplaced into a mold and then press-formed on dewatering, and a slurry ofcalcium silicate crystals free from any inactive substance and obtainedby a usual method is similarly press-formed in the mold over theresulting shaped body, or these procedures are performed in a reverseorder, whereby a laminated shaped body can be obtained.

The shaped body of the present invention thus obtained consistsessentially of globular shell-like secondary particles having an outsidediameter of about 5 to about 150 μm and formed of three-dimensionallyinterlocked calcium silicate crystals, voids interspersed between thesecondary particles, and an inactive substance physically united withthe secondary particles as enclosed therein or such inactive substanceand an amorphous siliceous substance. Although having a low density, theshaped body retains fully satisfactory strength for use and hasremarkably improved heat insulating properties over a wide temperaturerange due to the presence of the inactive substance in a large amount orof the inactive substance and the amorphous siliceous substance.

According to the present invention, desired lightweight shaped bodies ofcalcium silicate can be easily produced with low to high densities. Whena lightweight shaped body of low density, for example, a shaped bodyhaving a bulk density of 0.1 g/cm³ is to be preduced, it is desirable touse a lime milk having a sedimentation volume of at least 5 ml, moredesirably of at least 10 ml.

The sedimentation volume of a lime milk is determined by placing 50 mlof the lime milk as adjusted to a water to lime solids rario of 120:1into a messcylinder having an inside diameter of 1.3 cm and capacity of50 cm³, allowing the milk to stand for 20 minutes and then measuring thevolume in ml of the settled lime particles. A large sedimentation volumeindicates that the lime is effectively dispersible in water in a stablestate and is highly reactive. Use of a lime milk having a largersedimentation volume produces calcium silicate crystal secondaryparticles of lower apparent density, thus facilitating productionlightweight bodies of lower density.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention will be described below in greater detail withreference to the following examples and comparative examples, whereinthe parts and percentages are by weight. The properties were determinedby the following methods.

(a) Bending strength: According to the method of JIS A 9510.

(b) Thermal conductivity: According to the hollow cylindrical method ofJIS A 9510.

EXAMPLE 1

Quick lime (CaO 95%) was hydrated in hot water at 80° C. and dispersedin water by a homomixer to obtain a lime milk, which was 14.1 to 15.2 mlin sedimentation volume. To the lime milk was added a powder ofsiliceous stone (SiO₂ 94%), 6.5 μm in mean particle size, in theCaO/SiO₂ mole ratio of 1.00. Further added were water and a titaniumoxide powder (rutile, 2.3 μm in mean particle size) in such an amountthat the resulting shaped body would have a specified rutile content.Thus, a starting slurry was obtained which contained water in 15 timesthe amount by weight of the solids. The slurry was subjected to ahydrothermal synthesis reaction in an autoclave at a saturated watervapor pressure of 12 kg/cm² and a temperature of 191° C. for 5 hourswhile being stirred by a stirrer which was rotated at 40 r.p.m. In thisway, slurries of calcium silicate crystals were prepared.

Portions of the crystal slurries were dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analysis revealed the peak ofxonotlite crystals in all specimens and further the peak of rutilecrystals in the specimens containing titanium oxide particles.

When the crystal slurries were observed under an optical microscope aswell as under a scanning electron microscope, all the slurries werefound to contain globular shell-like secondary particles having anoutside diameter of 5 to 150 82 m and composed of three-dimensionallyinterlocked xonotlite crystals. With the slurries containing titaniumoxide particles, rutile crystals were found to have been physicallyunited with the secondary particles of xonotlite crystals as enclosedtherein.

FIGS. 1 and 2 show examples of optical photomicrographs FIG. 2 is aphotomicrograph (at a magnification of 250×) of the crystal slurryobtained according to the invention and containing rutile in such anamount as to give a rutile content of 25% by weight to the shaped bodyto be formed (one used for producing specimen No. 3 of shaped bodylisted in Table 1 below). FIG. 1 is a photomicrograph (at amagnification of 250×) of a rutile-free crystal slurry (one used forproducing specimen No. 1 of shaped body in Table 1). When compared withFIG. 1, FIG. 2 shows that the rutile is physically united with secondaryparticles of xonotlite crystals as enclosed therein.

Subsequently, 7 parts of glass fibers and 3 parts of portland cementwere added to 90 parts (solids) of each of the crystal slurries obtainedabove, and the mixture was pressed for dewatering and shaping and thendried at 100° C. to obtain a tubular shaped body, 114 mm in insidediameter, 50 mm in wall thickness and 610 mm in length.

The shaped bodies thus prepared were checked for structure by an opticalmicroscope and scanning electron microscope. All the bodies were foundto have been composed of a multiplicity of interconnected secondaryparticles of xonotlite crystals. In the bodies containing titanium oxideparticles, rutile crystals were physically united with the secondaryparticles as enclosed therein.

Table 1 shows the properties of the shaped bodies.

                                      TABLE 1                                     __________________________________________________________________________    Specimen No. 1   2   3   4   5   6   7   8                                    __________________________________________________________________________    Sedimentation volume                                                                       14.9                                                                              15.0                                                                              14.1                                                                              15.0                                                                              14.8                                                                              15.2                                                                              14.2                                                                              15.1                                 of lime milk (ml)                                                             Rutile content                                                                             0   15  25  35  45  55  65  75                                   (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                  0.150                                                                             0.148                                                                             0.151                                                                             0.150                                                                             0.147                                                                             0.153                                                                             0.150                                                                             0.149                                Bending strength                                                                           10.0                                                                              9.7 8.7 8.0 6.9 5.4 3.7 0.9                                  (kg/cm.sup.2)                                                                 Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C.                                                                             0.043                                                                             0.043                                                                             0.040                                                                             0.039                                                                             0.038                                                                             0.039                                                                             0.040                                                                             0.043                                150° C.                                                                             0.051                                                                             0.048                                                                             0.045                                                                             0.044                                                                             0.043                                                                             0.044                                                                             0.045                                                                             0.050                                250° C.                                                                             0.063                                                                             0.055                                                                             0.053                                                                             0.051                                                                             0.050                                                                             0.052                                                                             0.053                                                                             0.059                                350° C.                                                                             0.081                                                                             0.065                                                                             0.060                                                                             0.058                                                                             0.057                                                                             0.059                                                                             0.062                                                                             0.067                                __________________________________________________________________________

In Table 1, shaped body specimens Nos. 3 to 7 are according to theinvention, while specimes Nos. 1, 2 and 8 are shown for comparison.

Table 1 shows that the shaped bodies of the invention, ranging from 21to 70% in rutile content, have fully satisfactory strength for use andare further exceedingly lower in thermal conductivity over a widetemperature range than the rutile-free shaped body, specimen No. 1. Whencompared with the rutile-free shaped body, specimen No. 1, specimen No.2 having a low rutile content is lower in thermal conductivity at anaverage temperature of 150° C. or higher, but the reduction isinsufficient, and there is little or no reduction in thermalconductivity at an average temperature of 70° C. Specimen No. 8 whichconversely has a high rutile content is insufficient in the reduction ofthermal conductivity, has exceedingly low bending strength and is notactually usable.

EXAMPLE 2

Quick lime (CaO 95%) was hydrated in hot water at 80° C. and dispersedin water by a homomixer to obtain a lime milk, which was 13.5 to 15.2 mlin sedimentation volume. To the lime milk was added a powder ofsiliceous stone (SiO₂ 94%), 7.1 μm in mean particle size, in theCaO/SiO₂ mole ratio of 1.00. Further added were water and an iron oxidepowder (hematite, 0.51 μm in mean particle size) in such an amount thatthe resulting shaped body would have a specified hematite content. Thus,a starting slurry was obtained which contained water in 15 times theamount by weight of the solids. The slurry was subjected to ahydrothermal synthesis reaction in an autoclave at a saturated watervapor pressure of 12 kg/cm² and a temperature of 191° C. for 5 hourswhile being stirred by a stirrer which was rotated at 40 r.p.m. In thisway, slurries of calcium silicate crystals were prepared.

Portions of the crystal slurries were dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analysis revealed the peak ofxonotlite crystals in all specimens and further the peak of hematitecrystals in the specimens containing iron oxide particles.

When the crystal slurries were observed under an optical microscope aswell as under a scanning electron microscope, all the slurries werefound to contain globular shell-like secondary particles having anoutside diameter of 5 to 150 μm and composed of three-dimensionallyinterlocked xonotlite crystals. With the slurries containing iron oxideparticles, hematite crystals were found to have been physically unitedwith the secondary particles of xonotlite crystals as enclosed therein.

Subsequently, 7 parts of glass fibers and 3 parts of portland cementwere added to 90 parts (solids) of each of the crystal slurries obtainedabove, and the mixture was pressed for dewatering and shaping and thendried at 100° C. to obtain a tubular shaped body having the same shapeas those prepared in Example 1.

The shaped bodies thus prepared were checked for structure by an opticalmicroscope and scanning electron microscope. All the bodies were foundto have been composed of a multiplicity of interconnected secondaryparticles of xonotlite crystals. In the bodies containing iron oxideparticles, hematite crystals were physically united with the secondaryparticles as enclosed therein.

Table 2 shows the properties of the shaped bodies.

                                      TABLE 2                                     __________________________________________________________________________    Specimen No. 9   10  11  12  13  14  15  16                                   __________________________________________________________________________    Sedimentation volume                                                                       14.2                                                                              13.5                                                                              15.1                                                                              14.3                                                                              15.2                                                                              14.8                                                                              14.1                                                                              14.7                                 of lime milk (ml)                                                             Hematite content                                                                           0   15  25  35  45  55  65  75                                   (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                  0.151                                                                             0.149                                                                             0.150                                                                             0.151                                                                             0.153                                                                             0.150                                                                             0.149                                                                             0.151                                Bending strength                                                                           9.5 9.0 8.4 7.7 6.5 5.0 3.2 0.9                                  (kg/cm.sup.2)                                                                 Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C.                                                                             0.043                                                                             0.043                                                                             0.039                                                                             0.038                                                                             0.037                                                                             0.038                                                                             0.039                                                                             0.043                                150° C.                                                                             0.051                                                                             0.048                                                                             0.044                                                                             0.043                                                                             0.042                                                                             0.043                                                                             0.044                                                                             0.049                                250° C.                                                                             0.063                                                                             0.056                                                                             0.052                                                                             0.051                                                                             0.050                                                                             0.051                                                                             0.052                                                                             0.058                                350° C.                                                                             0.081                                                                             0.067                                                                             0.062                                                                             0.060                                                                             0.059                                                                             0.061                                                                             0.064                                                                             0.068                                __________________________________________________________________________

In Table 2, shaped body specimens Nos. 11 to 15 are according to theinvention, while specimens Nos. 9, 10 and 16 are shown for comparison.

Table 2 shows that the shaped bodies of the invention, ranging from 21to 70% in hematite content, have fully satisfactory strength for use andare further exceedingly lower in thermal conductivity over a widetemperature range than the hematite-free shaped body, specimen No. 9.When compared with the hematite-free shaped body, specimen No. 9,specimen No. 10 having a low hematite content is lower in thermalconductivity at an average temperature of 150° C. or higher, but thereduction is insufficient, and there is little or no reduction inthermal conductivity at an average temperature of 70° C. Specimen No. 16which conversely has a high hematite content is insufficient in thereduction of thermal conductivity, has exceedingly low bending strengthand is not actually usable.

EXAMPLE 3

Quick lime (32.0 parts, CaO 95%) was hydrated in 384 parts of hot waterat 80° C. and then dispersed in water by a homomixer to obtain a limemilk, which was 21.3 ml in sedimentation volume. To the lime milk wereadded 34.7 parts of siliceous stone powder (SiO₂ 94%) and 33.3 parts ofiron oxide powder (30% based on the shaped body) which were the same asthose used in Example 2. With addition of water to the mixture, astarting slurry was obtained which contained water in 20 times theamount by weight of the solids. The slurry was subjected to ahydrothermal synthesis reaction in an autoclave at a saturated watervapor pressure of 12 kg/cm² and a temperature of 191° C. for 5 hourswhile being stirred by a stirrer which was rotated at 40 r.p.m. In thisway, a slurry of calcium silicate crystals was prepared.

A portion of the crystal slurry was dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analaysis revealed the peaksof xonotlite and hematite crystals.

When the crystal slurry was observed under an optical microscope as wellas under a scanning electron microscope, the slurry was found to containglobular shell-like secondary particles having an outside diameter of 5to 150 μm and composed of three-dimensionally interlocked xonotlitecrystals. Hematite crystals were found to have been physically unitedwith the secondary particles of xonotlite crystals as enclosed therein.

Subsequently, 7 parts of glass fibers and 3 parts of portland cementwere added to 90 parts (solids) of the slurry, and the mixture waspressed for dewatering and shaping, and then dried at 100° C. to obtaintwo kinds of shaped bodies of the invention which were different in bulkdensity and having the same shape as those in Example 1 (specimens Nos.17 and 18).

The shaped bodies thus prepared were checked for structure by an opticalmicroscope and scanning electron microscope. Both the bodies were foundto have been composed of a multiplicity of interconnected secondaryparticles of xonotlite crystals. In the bodies, hematite crystals werephysically united with the secondary particles as enclosed therein.

For comparison, shaped bodies (specimen Nos. 19 and 20) of similar shapewere prepared in the same manner as above except that no iron oxidepowder was used.

Table 3 shows the properties of the shaped bodies obtained.

                  TABLE 3                                                         ______________________________________                                        Specimen No.   17       18      19     20                                     ______________________________________                                        Hematite content                                                                             30       30      0      0                                      (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                    0.105    0.203   0.104  0.203                                  Bending strength                                                                             5.1      15.3    6.1    18.2                                   (kg/cm.sup.2)                                                                 Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C. 0.038    0.043   0.042  0.048                                  150° C. 0.044    0.048   0.050  0.053                                  250° C. 0.054    0.052   0.065  0.063                                  350° C. 0.065    0.060   0.084  0.077                                  ______________________________________                                    

COMPARATIVE EXAMPLE 1

Quick lime (CaO 95%) was hydrated in hot water at 80° C. to obtain alime milk, to which a siliceous stone powder (SiO₂ 94%) was added in theCaO/SiO₂ mole ratio of 1.00. Further added to the mixture were the sameiron oxide powder (hematite) as used in Example 2 in a specified amountbased on the shaped body to be formed, and chrysotile asbestos in anamount of 20% based on the shaped body. With addition of water, astarting slurry was prepared which contained water in 7 times the amountby weight of the solids. The slurry was placed into a tubular mold, 114mm in inside diameter, 50 in wall thickness and 610 mm in length, andthen subjected to a hydrothermal synthesis reaction at a saturated watervapor pressure of 15 kg/cm² and at a temperature of 200° C. for 6 hours.

After the reaction, the mold was withdrawn, and the product was removedfrom the mold and dried. The shaped body obtained was found to have beencomposed of xonotlite crystals by X-ray diffraction method. Whenfractured surfaces of shaped bodies similarly prepared were observedunder an optical microscope and scanning electron microscope to checkthe bodies for the structure, no secondary particles of xonotlitecrystals were found.

Table 4 shows the properties, etc.

                  TABLE 4                                                         ______________________________________                                        Specimen No.   21        22      23      24                                   ______________________________________                                        Hematite content                                                                             0         10      20      25                                   (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density   0.153     0.156   0.165   *.sup.1                              (g/cm.sup.3)                                                                  Bending strength                                                                             4.2       2.2     1.3                                          (kg/cm.sup.2)                                                                 ______________________________________                                         *.sup.1 Even if it was attempted to attain a bulk density of 0.16 or 0.20     the reaction failed to give a shaped body of desired dimensions owing to      the sedimentation of solids in the mold.                                 

Table 4 shows that with the shaped bodies which were obtained by shapinga hematite-containing starting slurry and subjecting the shaped body tohydrothermal reaction and in which no secondary particles of xonotlitecrystals were present, the bending strength decreases markedly withincreasing hematite content, with the result that the body fails to havestrength for use when 20% of hematite is present. It is seen that above25%, lightweight bodies about 0.16 or 0.20 g/cm³ in bulk density are nolonger obtainable.

COMPARATIVE EXAMPLE 2

A slurry of calcium silicate crystals was prepared in the same manner asin Example 1 except that no titanium oxide powder was used.

A portion of the crystal slurry was dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analysis revealed the peak ofxonotlite crystals. When the slurry was dried on slide glass andobserved under an optical microscope, globular secondary particles werefound which were 5 to 150 μm in outside diameter.

Subsequently, to 90 parts (solids) of the slurry were added 7 parts ofglass fibers, 3 parts of portland cement and the same titanium oxidepowder as used in Example 1 in an amount of 25% by weight or 40% byweight based on the shaped body to be obtained. The mixtures thusprepared were pressed for dewatering and shaping, and then dried at 100°C. to obtain comparative shaped bodies of the same shape as thoseobtained in Example 1.

Table 5 shows the properties of the shaped bodies.

                  TABLE 5                                                         ______________________________________                                        Specimen No.   25      26      27                                             ______________________________________                                        Rutile content 0       25      40                                             (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density   0.150   0.151   Failed to form a                               (g/cm.sup.3)                   shaped body having                             Bending strength                                                                             9.8     1.3     a bulk density of                              (kg/cm.sup.2)                  about 0.15.                                    ______________________________________                                    

Table 5 shows that when more than 20% by weight of titanium oxide powderwas added to the slurry after the hydrothermal synthesis reaction,markedly impaired bending strength resulted.

COMPARATIVE EXAMPLE 3

A starting slurry prepared in the same manner as in Comparative Example2 except that the slurry contained water in 30 times the amount byweight of the solids was subjected to a hydrothermal synthesis reactionin an autoclave at a saturated water vapor pressure of 15 kg/cm² and atemperature of 200° C. for 2 hours while being stirred by a stirrerwhich was driven at 40 r.p.m. to prepare an aqueous slurry consistingprimarily of C--S--H (I).

Comparative shaped bodies having the same shape as those in Example 1were prepared by adding to 93 parts (solids) of the slurry obtainedabove 7 parts of alkali-resistant glass fibers singly, or in combinationwith 25% by weight or 40% by weight, based on the shaped body, of thesame titanium oxide powder as used in Example 1, and pressing themixture for dewatering and shaping. The shaped bodies were cured withsteam at a saturated water vapor pressure of 15 kg/cm² for 3 hours andthereafter dried at 100° C.

The shaped bodies were analyzed by X-ray diffractometer. The analysisrevealed the peak of xonotlite crystals in all the bodies and furtherthe peak of rutile crystals in the bodies containing titanium oxideparticles.

Table 6 shows the properties of the bodies.

                  TABLE 6                                                         ______________________________________                                        Specimen No.   28      29      30                                             ______________________________________                                        Rutile content 0       25      40                                             (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density   0.151   0.151   Failed to form a                               (g/cm.sup.3)                   shaped body having                             Bending strength                                                                             8.0     1.1     a bulk density of                              (kg/cm.sup.2)                  about 0.15.                                    ______________________________________                                    

Table 6 shows that when the slurry of C--S--H (I) contains titaniumoxide powder added thereto and is shaped, the shaped body exhibitsseriously impaired bending strength even if cured with steam aftershaping.

COMPARATIVE EXAMPLE 4

An aqueous slurry comprising C--S--H (I) and rutile crystals wasprepared in the same manner as in Comparative Example 3 with theexception of adding to the starting slurry the same titanium oxidepowder as used in Example 1, in an amount of 15% or 25% based on theshaped body to be obtained.

Subsequently, 7 parts of alkali-resistant glass fibers the same as thoseused in Comparative Example 3 were added to 93 parts (solids) of theslurry obtained above, and the mixture was pressed for dewatering andshaping, giving a comparative shaped body of the same shape as those inExample 1. The shaped body was cured with steam at a saturated watervapor pressure of 15 kg/cm² for 3 hours and thereafter dried at 100° C.

When the shaped body obtained was checked by X-ray diffraction method,the peaks of xonotlite crystals and rutile crystals were observed.

The shaped body markedly deformed or shrank on drying, failing to retainthe desired shape.

The above result indicates that when not smaller than about 15% oftitanium oxide powder is present, shaped bodies are difficult to produceby the process comprising pre-reacting a starting slurry containingtitanium oxide particles to obtain a slurry of C--S--H (I), shaping theslurry and curing the shaped body with steam.

EXAMPLE 4

Quick lime (32 parts, CaO 95%) was hydrated in 384 parts of hot water at80° C. and then dispersed in water by a homomixer to obtain a lime milk,which was 15 to 16 ml in sedimentation volume. To the lime milk wereadded 34.7 parts of siliceous stone powder (SiO₂ 94%) having a meanparticle size of 6.5 μm and 33.3 parts (30% based on the shaped body tobe obtained) of the inactive substance listed in Table 7. With additionof water to the mixture, a starting slurry was obtained which containedwater in 15 times the amount by weight of the solids. The slurry wassubjected to a hydrothermal synthesis reaction in an autoclave at asaturated water vapor pressure of 12 kg/cm² and a temperature of 191° C.for 5 hours while being stirred by a stirrer which was driven at 40r.p.m. In this way, slurries of calcium silicate crystals were prepared.

Portions of the crystal slurries were dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analysis revealed the peaksof xonotlite crystals and the above inactive substance.

When the crystal slurries were observed under an optical microscope andscanning electron microscope, all the slurries were found to containglobular shell-like secondary particles having an outside diameter of 5to 150 μm and composed of three-dimensionally interlocked xonotitecrystals. With the slurry containing the inactive substance, theinactive substance was found to have been physically united withsecondary particles of xonotlite crystals as enclosed therein.

To check the shaped bodies obtained for the structure, fracturedsurfaces of these bodies were observed under an optical microscope andscanning electron microscope. Consequently, all the shaped bodies werefound to have been composed of a multiplicity of interconnectedsecondary particles of xonotlite crystals. With those containingtheinactive substance, the substance was found to have been physicallyunited with the secondary particles as enclosed therein.

Table 7 shows the properties of the shaped bodies obtained.

                                      TABLE 7                                     __________________________________________________________________________    Specimen No.  31   32  33    34    35                                         __________________________________________________________________________    Inactive substance                                                            Name          Silicon                                                                            Silicon                                                                           Titanium                                                                            Zirconium                                                                           None                                                     carbide                                                                            carbide                                                                           oxide oxide                                                                   (rutile)                                               Mean particle size (μm)                                                                  3.5  42  0.15  4.5                                              Content (in shaped body, %)                                                                 30   30  30    30    0                                          Sedimentation volume                                                                        15.0 15.4                                                                              15.3  15.1  16.0                                       of lime milk (ml)                                                             Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                   0.149                                                                              0.150                                                                             0.148 0.151 0.149                                      Bending strength (kg/cm.sup.2)                                                              8.0  7.5 7.9   8.1   9.4                                        Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C.                                                                              0.038                                                                              0.039                                                                             0.039 0.038 0.043                                      150° C.                                                                              0.043                                                                              0.045                                                                             0.047 0.045 0.051                                      250° C.                                                                              0.051                                                                              0.054                                                                             0.057 0.055 0.063                                      350° C.                                                                              0.058                                                                              0.063                                                                             0.068 0.067 0.080                                      __________________________________________________________________________

Further shaped bodies comparable to the above bodies in properties wereobtained using silicon nitride, calcium silicide, tin oxide andmanganese oxide in the same manner as above.

EXAMPLE 5

Quick lime (38.4 parts, CaO 95%) was hydrated in 474 parts of hot waterat 80° C. and then dispersed in water by a homomixer to obtain a limemilk, which was 18 ml in sedimentation volume. To the lime milk wereadded 41.6 parts of siliceous stone powder (SiO₂ 94%) having a meanparticle size of 7.4 μm and 20.0 parts (15.0% based on the shaped bodyto be obtained) of iron oxide powder (hematite), 0.51 μm in meanparticle size. With addition of water to the mixture, a starting slurrywas obtained which contained water in 20 times the amount by weight ofthe solids. The slurry was subjected to a hydrothermal synthesisreaction in an autoclave at a saturated water vapor pressure of 12kg/cm² and a temperature of 191° C. for 5 hours while being stirred by astirrer which was driven at 40 r.p.m. In this way, a slurry of calciumsilicate crystals was prepared.

A portion of the crystal slurry was dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analysis revealed the peaksof xonotlite crystals and hematite crystals.

When the crystal slurry was observed under an optical microscope andscanning electron microscope, the slurry was found to contain globularshell-like secondary particles having an outside diameter of 5 to 150 μmand composed of three-dimensionally interlocked xonotlite crystals.Hematite crystals were found to have been physically united withsecondary particles of xonotlite crystals as enclosed therein.

Subsequently, to 75 parts (solids) of the crystal slurry obtained abovewere added 10 parts of white carbon (trademark "Tokusil GU," product ofTokuyama Soda Co., Ltd., 0.02 to 0.04 μm in particle size) and theadditives of 7 parts of glass fibers, 5 parts of pulp and 3 parts ofportland cement. The mixture was pressed for dewatering and shaping, andthen dried at 100° C., giving a shaped body (specimen No. 36) of theinvention having the same shape as those in Example 1. Further a shapedbody (specimen No. 37) of the invention having like shape was preparedin the same manner as above with the exception of using Opsil-II, 10 to60 μm in outside diameter, in place of white carbon.

Table 8 below shows the properties of the shaped bodies.

Opsil-II was prepared in the same manner as in Example 6 disclosed inU.S. Pat. No. 4,230,765, i.e. by the follwing procedure. A slurry ofxonotlite crystals obtained by hydrothermal synthesis reaction wasdewatered to the water to solids (xonotlite crystals) ratio of 5/1 byweight, then placed into a container having a wet atmosphere and reactedfor about 30 minutes with carbon dioxide gas forced into an internalpressure of 3 kg/cm². Subsequently, the reaction mixture was treatedwith 6N hydrochloric acid solution for 1 minute and thereafterthoroughly washed with water to completely dissolve out calciumchloride, giving a slurry of bulky amorphous silica gel secondaryparticles having an outside diameter of 10 to 60 μm. The slurry wasdried and used as Opsil-II.

COMPARATIVE EXAMPLE 5

By the same procedure as used for producing the shaped body, specimenNo. 36, of Example 5, a comparative shaped body (specimen No. 38) ofsimilar shape was prepared without using any iron oxide powder or whitecarbon.

A comparative shaped body (specimen No. 39) of similar shape wasprepared in the same manner as specimen No. 36 with the exception ofusing no white carbon and using 17.15 parts of iron oxide powder to givean iron oxide content of 15% to the shaped body.

A comparative shaped body (specimen No. 40) of similar shape wasprepared in the same manner as specimen No. 37 except that no iron oxidepowder was used.

A comparative shaped body (specimen No. 41) of similar shape wasprepared in the same manner as specimen No. 36 except that white carbon,which is an amorphous silica, was replaced by a siliceous stone powder(4 μm in mean particle size) which is a crystalline silica.

A comparative shaped body (specimen No. 42) of similar shape wasprepared in the same manner as specimen No. 36 with the exception ofconducting the hydrothermal reaction without adding iron oxide powder tothe starting slurry and adding to the resulting slurry iron oxide powderand white carbon each in the same amount as used for specimen No. 36.

For each specimen of Comparative Example 5, the additives (glassfiber:pulp:portland cement=7:5:3) were used in such a combined amount asto give an additive content of 15% to the shaped body as in Example 5.

Table 8 shows the properties of the shaped bodies obtained in Example 5and Comparative Example 5.

                                      TABLE 8                                     __________________________________________________________________________                 Example 5                                                                             Comparative Example 5                                    Specimen No. 36  37  38  39  40  41  42                                       __________________________________________________________________________    Hematite content                                                                           15  15  0   15  0   15  15**                                     (in shaped body, %)                                                           Content of amorphous                                                                       10  10  0   0   10  0*  10                                       siliceous substance                                                           (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                  0.112                                                                             0.111                                                                             0.113                                                                             0.110                                                                             0.113                                                                             0.120                                                                             0.114                                    Bending strength (kg/cm.sup.2)                                                             4.5 6.0 6.3 6.1 6.2 3.2 1.2                                      Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C.                                                                             0.038                                                                             0.038                                                                             0.042                                                                             0.041                                                                             0.039                                                                             0.042                                                                             0.039                                    150° C.                                                                             0.044                                                                             0.044                                                                             0.049                                                                             0.046                                                                             0.047                                                                             0.046                                                                             0.045                                    250° C.                                                                             0.057                                                                             0.057                                                                             0.064                                                                             0.058                                                                             0.064                                                                             0.058                                                                             0.057                                    350° C.                                                                             0.071                                                                             0.071                                                                             0.085                                                                             0.072                                                                             0.086                                                                             0.072                                                                             0.071                                    __________________________________________________________________________     Note:                                                                         *Containing 10% of crystalline silica.                                        **Added after hydrothermal synthesis reaction.                           

Table 8 shows that by adding an inactive substance to the startingslurry to be subjected to hydrothermal synthesis reaction and anamorphous siliceous substance to the slurry resulting from the reaction,shaped bodies of calcium silicate can be obtained which retain fullysatisfactory strength for use and which further exhibit a remarkablyreduced thermal conductivity over a wide temperature range of from lowto high temperatures even when the content of inactive substance is 15%.

It is also seen that the use of Opsil-II results in higher strength thanwhen white carbon is used.

EXAMPLE 6

Quick lime (38.4 parts, CaO 95%) was hydrated in 474 parts of hot waterat 80° C. and then dispersed in water by a homomixer to obtain a limemilk, which was 17 to 20 ml in sedimentation volume. To the milk wereadded 416 parts of siliceous stone powder (SiO₂ 95%) having a meanparticle size of 6.5 μm and 20.0 parts (15% based on the shaped body tobe obtained) of the inactive substance listed in Table 9. The mixturewas subjected to a hydrothermal synthesis reaction in the same manner asin Example 5. In this way, slurries of calcium silicate crystals wereprepared.

Portions of the crystal slurries were dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analysis revealed the peaksof xonotlite crystals and the above inactive substance.

When the crystal slurries were observed under an optical microscope andscanning electron microscope, all the slurries were found to containglobular shell-like secondary particles having an outside diameter of 5to 150 μm and composed of three-dimensionally inter-locked xonotlitecrystals, with the inactive substance physically united with thesecondary particles of xonotlite crystals as enclosed therein.

Subsequently, to 75 parts (solids) of each crystal slurry thus obtainedwere added 10 parts of the amorphous siliceous substance listed in Table9 below, and the additives of 7 parts of glass fibers, 5 parts of pulpand 3 parts of portland cement. The mixture was dewatered and shaped bya press and then dried at 100° C. Thus, shaped bodies of this inventionwere prepared in the same shape as those in Example 1.

Table 9 shows the properties of the shaped bodies.

                                      TABLE 9                                     __________________________________________________________________________    Specimen No.  43   44   45   46  47    48   49   50     51                    __________________________________________________________________________    Inactive substance                                                                          Graphite                                                                           Silicon                                                                            Titanium                                                                           Silicon                                                                           Manganese                                                                           Titanium                                                                           Tin oxide                                                                          Boron  Iron oxide                               carbide                                                                            oxide                                                                              nitride                                                                           oxide carbide   nitride                                                                              (hematite)                                    (rutile)                                              Mean particle size (μm)                                                                  7.5  3.5  0.26 5.0 4.0   5.0  6.2  6.0    7.4                   Content (in shaped body, %)                                                                 15   15   15   15  15    15   15   15     15                    Sedimentation volume                                                                        17   19   18   20  17    17   20   19     19                    of lime milk (ml)                                                             Amorphous siliceous                                                                         Opsil-II                                                                           Opsil-II                                                                           Opsil-II                                                                           Ferro-                                                                            Fly ash                                                                             Ferro-                                                                             Opsil-II                                                                           Diatomaceous                                                                         Diatomaceous          substance                    silicon   silicon   earth  earth                                              dust      dust                                   Particle size (μm)                                                                       10˜60                                                                        10˜60                                                                        10˜60                                                                        0.24                                                                              4˜44                                                                          0.24 10˜60                                                                        1˜50                                                                           1˜50                          (Outside                                                                           (Outside                                                                           (Outside                                                                           (Mean)    (Mean)                                                                             (Outside                                        diameter)                                                                          diameter)                                                                          diameter)           diameter)                         Content (in shaped body, %)                                                                 10    10  10   10  10    10   10   10     10                    Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                   0.111                                                                              0.110                                                                              0.112                                                                              0.112                                                                             0.111 0.114                                                                              0.109                                                                              0.109  0.114                 Bending strength (kg/cm.sup.2)                                                              6.2  5.9  6.1  4.6 4.8   4.6  6.1  4.7    4.5                   Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C.                                                                              0.038                                                                              0.038                                                                              0.039                                                                              0.038                                                                             0.038 0.039                                                                              0.038                                                                              0.039  0.038                 150° C.                                                                              0.044                                                                              0.044                                                                              0.045                                                                              0.045                                                                             0.045 0.045                                                                              0.044                                                                              0.044  0.044                 250° C.                                                                              0.054                                                                              0.054                                                                              0.059                                                                              0.055                                                                             0.056 0.058                                                                              0.055                                                                              0.055  0.054                 350° C.                                                                              0.072                                                                              0.065                                                                              0.076                                                                              0.067                                                                             0.072 0.076                                                                              0.073                                                                              0.070  0.065                 __________________________________________________________________________

Opsil-II in Table 9 is the same as the one used in Example 5.

Table 9 shows that various different combinations of inactive substanceand amorphous siliceous substance also afford shaped bodies retainingfully satisfactory strength for use and a remarkably reduced thermalconductivity over a wide temperature range.

EXAMPLE 7

To 65 parts (solids) of a slurry of calcium silicate crystals preparedin the same manner as in Example 5 were added 20 parts of white carbon(trademark "Nipsil VN3," product of Nippon Silica Industrial Co., Ltd.,mean particle size of 0.016 μm), and the additives of 7 parts of glassfibers, 5 parts of pulp and 3 parts of portland cement. The mixture wasdewatered and shaped by a press, and then dried at 100° C. Thus shapedbodies of the invention were prepared in the same shape as those ofExample 1. The hematite content of the resulting shaped bodies was 13%.

Table 10 shows the properties of the shaped bodies.

                  TABLE 10                                                        ______________________________________                                        Specimen No.        52      53                                                ______________________________________                                        Hematite content    13      13                                                (in shaped body, %)                                                           White carbon content                                                                              20      20                                                (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                         0.110   0.155                                             Bending strength (kg/cm.sup.2)                                                                    4.1     8.8                                               Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C.      0.037   0.039                                             150° C.      0.043   0.045                                             250° C.      0.057   0.055                                             350° C.      0.072   0.067                                             ______________________________________                                    

EXAMPLE 8

Quick lime (33.0 parts, CaO 95%) was hydrated in 396 parts of hot waterat 80° C. and then dispersed in water by a homomixer to obtain a limemilk, which was 23.6 ml in sedimentation volume. To the milk were added35.7 parts of the same siliceous stone powder as used in Example 5 and31.3 parts (25.0% baed on the shaped body to be obtained) of the sameiron oxide powder (hematite) as used in Example 5. With addition ofwater to the mixture, a starting slurry was obtained which containedwater in 20 times the amount by weight of the solids. The slurry wassubjected to a hydrothermal synthesis reaction in an autoclave at asaturated water vapor pressure of 12 kg/cm² and a temperature of 191° C.for 5 hours while being stirred by a stirrer which was driven at 40r.p.m. In this way, a slurry of calcium silicate crystals was prepared.

A portion of the crystal slurry was dried at 100° C. for 24 hours andthen analyzed by X-ray diffractometer. The analysis revealed the peaksof xonotlite crystals and hematite crystals.

When the crystal slurry was observed under an optical microscope andscanning electron microscope, the slurry was found to contain globularshell-like secondary particles having an outside diameter of 5 to 150 μmand composed of three-dimensionally interlocked xonotlite crystals, withhematite crystals physically united with the xonotlite crystal secondaryparticles as enclosed therein.

Subsequently, to 80 parts (solids) of the slurry thus obtained wereadded 10 parts of Opsil-II, the same as the one used in Example 5, andthe additives of 7 parts of glass fibers and 3 parts of cement. Themixture was shaped by a press and then dried at 100° C. In this way, twokinds of shaped bodies (specimen No. 54 and 55) were prepared which weredifferent in bulk density and in the same shape as those of Example 1.Table 11 shows the properties.

COMPARATIVE EXAMPLE 6

By the same procedure as Example 8, comparative shaped bodies (specimenNos. 56 and 57) were prepared in a similar shape except that the limemilk was 18 ml in sedimentation volume and that no iron oxide powder orOpsil-II was used.

Comparative shaped bodies (specimen Nos. 58 and 59) of similar shapewere prepared in the same manner as in Example 8 except that the limemilk was 18 ml in sedimentation volume and that no iron oxide powder wasused.

In Comparative Example 6, the additives (glass fibers:cement=7:3) wereused in such a combined amount as to give an additive content of 10% tothe shaped bodies as in Example 8.

Table 11 shows the properties of the shaped bodies obtained in Example 8and Comparative Example 6.

                                      TABLE 11                                    __________________________________________________________________________                 Example 8                                                                              Comparative Example 6                                   Specimen No. 54   55  56   57  58   59                                        __________________________________________________________________________    Hematite content                                                                           25   25  0    0   0    0                                         (in shaped body, %)                                                           Opsil-II content                                                                           10   10  0    0   10   10                                        (in shaped body, %)                                                           Properties of shaped body                                                     Bulk density (g/cm.sup.3)                                                                  0.148                                                                              0.201                                                                             0.149                                                                              0.200                                                                             0.150                                                                              0.201                                     Bending strength (kg/cm.sup.2)                                                             8.4  15.0                                                                              11.2 17.8                                                                              10.3 17.7                                      Thermal conductivity                                                          (Kcal/m · hr. °C.)                                            Average temp.                                                                  70° C.                                                                             0.037                                                                              0.040                                                                             0.043                                                                              0.047                                                                             0.041                                                                              0.045                                     150° C.                                                                             0.042                                                                              0.045                                                                             0.051                                                                              0.052                                                                             0.051                                                                              0.051                                     250° C.                                                                             0.050                                                                              0.052                                                                             0.063                                                                              0.062                                                                             0.065                                                                              0.064                                     350° C.                                                                             0.060                                                                              0.059                                                                             0.081                                                                              0.076                                                                             0.084                                                                              0.079                                     __________________________________________________________________________

We claim:
 1. A calcium silicate shaped body comprising a multiplicity ofinterconnected secondary particles of calcium silicate crystals, voidsinterspersed between the secondary particles, and at least one inorganicinactive substance selected from among carbonaceous substance, carbide,nitride, silicide and metallic oxide and physically united with thesecondary particles, the shaped body containing the inactive substancein an amount of 21 to 70% by weight.
 2. A shaped body as defined inclaim 1 wherein the inactive substance is physically united with thesecondary particles of calcium silicate crystals as enclosed therein. 3.A shaped body as defined in claim 1 wherein the secondary particles ofcalcium silicate crystals are originally in the form of substantiallyglobular shells having an outside diameter of about 5 to about 150 μmand formed of three-dimensionally interlocked calcium silicate crystals.4. A shaped body as defined in claim 1 which contains the inactivesubstance in an amount of 25 to 55% by weight.
 5. A shaped body asdefined in claim 1 wherein the carbonaceous substance is at least one ofactive carbon, charcoal, coal, carbon black and graphite, the carbidebeing at least one of silicon carbide, boron carbide and titaniumcarbide, the nitride being at least one of silicon nitride, boronnitride and titanium nitride, the silicide being calcium silicide, themetallic oxide being at least one of iron oxide, titanium oxide, tinoxide, manganese oxide, zirconium oxide, ilmenite, zircon and chromite.6. A shaped body as defined in claim 1 wherein the calcium silicatecrystals are tobermorite crystals and/or xonotlite crystals.
 7. Acalcium silicate shaped body comprising a multiplicity of interconnectedsecondary particles of calcium silicate crystals, voids interspersedbetween the secondary particles, at least one inorganic inactivesubstance selected from among carbonaceous substance, carbide, nitride,silicide and metallic oxide and physically united with the secondaryparticles, and an amorphous siliceous substance.
 8. A shaped body asdefined in claim 7 wherein the inactive substance is physically unitedwith the secondary particles of calcium silicate crystals as enclosedtherein.
 9. A shaped body as defined in claim 7 wherein the secondaryparticles of calcium silicate crystals are originally in the form ofsubstantially globular shells having an outside diameter of about 5 toabout 150 μm and formed of three-dimensionally interlocked calciumsilicate crystals.
 10. A shaped body as defined in claim 7 wherein thecarbonaceous substance is at least one of active carbon, charcoal, coal,carbon black and graphite, the carbide being at least one of siliconcarbide, boron carbide and titanium carbide, the nitride being at leastone of silicon nitride, boron nitride and titanium nitride, the silicidebeing calcium silicide, the metallic oxide being at least one of ironoxide, titanium oxide, tin oxide, manganese oxide, zirconium oxide,ilmenite, zircon and chromite.
 11. A shaped body as defined in claim 7which contains the inactive substance in an amount of 2 to 60% byweight.
 12. A shaped body as defined in claim 11 which contains theinactive substance in an amount of 5 to 50% by weight.
 13. A shaped bodyas defined in claim 7 wherein the amorphous siliceous substance is atleast one of white carbon, ferrosilicon dust, silicon dust, diatomaceousearth, fly ash and silica gel.
 14. A shaped body as defined in claim 7wherein the amorphous siliceous substance is Opsil-II.
 15. A shaped bodyas defined in claim 7 which contains the amorphous siliceous substancein an amount of 2 to 60% by weight.
 16. A shaped body as defined inclaim 15 which contains the amorphous siliceous substance in an amountof 5 to 50% by weight.
 17. A shaped body as defined in claim 7 whichcontains the inactive substance and the amorphous siliceous substance ina combined amount of 4 to 70% by weight.
 18. A shaped body as defined inclaim 17 which contains the inactive substance and the amorphoussiliceous substance in a combined amount of 10 to 50% by weight.
 19. Ashaped body as defined in claim 7 wherein the calcium silicate crystalsare tobermorite crystals and/or xonotlite crystals.